The present invention relates to a screw joint of the kind intended for holding together two components which are arranged for rapid rotation about the centre axis of the joint and of which screw joint the mutually co-acting screw threads have a profile that exhibits flank surfaces inclined relative to said centre axis. The components are so arranged that when rotating at least one of (a) the forces transmitted by the screw joint and (b) the centrifugal forces acting on the components constitutes a deforming load on the screw joint which, if not compensated for, is liable to result in an uneven distribution of load between the various screw threads of the screw joint.
As a result of varying axial deformation occurring in the screw-joint material when the joint is under tension, the major part of the force transmitted by the screw joint is normally concentrated on a few screw threads thereof, while other screw threads of the joint are only subjected to a relatively slight load. For example, in the case of a conventional nut and screw joint, 50% of the load lies on a first screw thread, 25% of the load lies on the next screw thread and 12.5% of the load lies on the next following screw thread, whereas the remaining screw threads are relatively free of load. Since the distribution of load between the screw threads influences the dynamic strength of the screw joint, the aforementioned uneven load distribution on the screw threads causes the majority of fatigue fractures to occur at the "first" load-bearing thread. Consequently, the useful life of a screw thread could be extended considerably, if it were possible to relieve the load on this "first" screw thread, this first screw thread normally taking 50% of the total load.
Attempts to achieve more uniform distribution of the load on the screw threads of a screw joint have been made in the past by designing the nut in a particular manner, such that the pressure-activated surface is located, for steering the force flow, so that the load is distributed as uniformly as possible over a plurality of screw threads.
It is true of all types of screw joints which incorporate screw threads that have flank surfaces which slope in relation to the longitudinal axis that the axial contact between two mutually co-acting screw threads is influenced by the mutual radial position of the threads. Thus, the distribution of load between the screw threads of a screw joint can be influenced by changing the mutual radial position between the screw threads, as this will cause a change in the axial distance between mutually co-acting screw threads. Earlier attempts have been made to utilize this fact in a manner to obtain a uniform distribution of the load on a stationary screw joint, by providing one of the screw-threaded components of the screw joint with a conical screw thread along at least a part of its axial extension, c.f. for example GB-A-2 074 280. It is also possible by means of a suitable load to obtain a corresponding deformation of, e.g., a nut.